Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of the first image in a sequence of a display screen or portion thereof with transitional graphical user interface, showing our new design; and,

FIG. 2 is a front view of the second image thereof.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1-2. The process or period in which one image transitions to another forms no part of the claimed design.

The outer perimeter illustrated by dashed broken lines in the drawings represents a display screen or portion thereof and forms no part of the claimed design. The remaining dashed broken lines shown in the drawings depict portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 